Novel strategy of immunizing a phosphorylated peptide or a synthetic phosphopeptide, which corresponds to the protein phosphorylated at a targeted residue. Method has been applied to the production of antibodies that can specifically recognize the other types of site-specific protein modification, such as acetylation, methylation, and proteolysis. - [Read Functional Analyses for Site-Specific Phosphorylation of a Target Protein in Cells]